MAX8794 Datasheet, PDF (10/13 Pages) Maxim Integrated Products – Low-Voltage DDR Linear Regulator

Low-Voltage DDR Linear Regulator
SHDN
200µs
CURRENT LIMIT
POWER-GOOD
WINDOW
OUTPUT OVERLOAD
CONDITION
OUT
PGOOD
2ms STARTUP
DELAY
10µs
PROPAGATION
DELAY
10µs
PROPAGATION
DELAY
Figure 3. MAX8794 PGOOD and Soft-Start Waveforms
Power-Good (PGOOD)
The MAX8794 provides an open-drain PGOOD output
that goes high 2ms (typ) after the output initially reach-
es regulation during startup. PGOOD transitions low
10µs after the output goes out of regulation by ±150mV,
or when the device enters shutdown. Connect a pullup
resistor from PGOOD to V_CC for a logic-level output.
Use a 100kΩ resistor to minimize current consumption.
Applications Information
Dynamic Output-Voltage Transitions
By changing the voltage at REFIN, the MAX8794 can
be used in applications that require dynamic output-
voltage changes between two set points (graphics
processors). Figure 4 shows a dynamically adjustable
resistive voltage-divider network at REFIN. Using an
external signal MOSFET, a resistor can be switched in
and out of the REFIN resistor-divider, changing the volt-
age at REFIN. The two output voltages are determined
by the following equations:
V_OUT(LOW)
=
V_REF
⎛ _R2 ⎞
⎝⎜ ^{R1 + R2}⎠⎟
⎡ _{(R2 + R3)} ⎤
( ) ^VOUT(HIGH)
=
V_REF
⎢
⎣⎢^R1
+
R2
+ R3
⎥
⎦⎥
REFERENCE
VOLTAGE
(V_REF)
R1
C_REFIN
R2
MAX8794
REFIN
V_OUT(LOW)
V_OUT(HIGH)
R3
( )^R2
V_OUT(LOW) = V_{REF R1 + R2}
(R2 + R3)
V_OUT(HIGH) = VREF _{R1 + (R2 + R3)}
Figure 4. Dynamic Output-Voltage Change
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